1. Field of the Invention
The present invention relates to an optical pen having a light path coaxial with its pen tip, in particular a kind of optical pen that integrates the functions of optical mouse and handwriting recognition where the path of captured imaging light is coaxial with the pen tip.
2. Description of the Prior Art
For electronic information devices such as desktop or notebook computers, personal digital assistants (PDA), and smart phones that require massive data input, handwriting input device is undoubtedly a convenient alternative to mouse and keyboard.
Currently known handwriting input devices may be classified into three types; one needs to be used with pressure-sensing touch screen, one uses electromagnetic-sensing digital panel, and one uses optical pen. Optical pen is the more popular handwriting input device at the present time due to its relatively low cost and the ability to write on any surface.
FIG. 1 is a schematic view of conventional optical pen 10, which is essentially an optical mouse in the shape of a pen. The shaft of the pen 11 makes it easy for the users to hold the pen when writing, while light source 12 and optical sensor 13 arranged at the bottom of the body 11 can capture the reflected image in a small area 16 on an outlying surface 15 near the tip of the pen 14. When the optical pen 10 moves, the captured images will undergo continuous and directional changes, from which the moving directions and speed of optical pen 10 are detected. By transmitting such information to an electronic information device connected to the optical pen 10 for processing, handwriting input is achieved.
However conventional optical pen 10 as shown in FIG. 1 has an apparent drawback. FIG. 2A and FIG. 2B depict respectively the position of light path of optical pen 10 (FIG. 1) relative to pen tip 14 and the position of pen tip 14 relative to images of the small area 16 captured by optical sensor 13 when optical pen 10 moves. In light that the axial direction 17 of pen tip 14 of conventional optical pen 10 is not the same as (not overlapping with) that of the light path 18 of images captured by optical sensor 13 (i.e. light traveling path), there is a spacing d between the pen tip 14 and the images of the small area 16 captured by optical sensor 13. When the user of optical pen 10 writes, the optical pen 10 generates rotational movement (as shown in FIG. 2B), during which the traveling speed, direction and distance of images captured by optical sensor 13 are different from those of pen tip 14. Consequently, the pen tip 14 travels in straight line, while the images of the small area 16 captured by optical sensor 13 move along a curved arc. When the pen makes turns (i.e. not writing in straight line), the images of text or graph captured by optical sensor 13 are prone to distortion or result in discontinuous lines. Such drawback needs improvement.